| 摘要 |
PURPOSE:To eliminate the need for a thinning filter by driving a digital signal processing part with the clock pulse of the frequency in accordance with the Nyquist frequency of the low pass filter for removing a calling signal at the time of a ring trip processing. CONSTITUTION:At the time of processing sound, changing-over switches 31 and 37 are respectively selected at an SA side and a C2M side, and through an AD converter 32 and a thinning filter 33, a sound processing is executed by a digital signal processing circuit 36. At the time of the ring trip processing, the changing-over switches 31 and 37 are respectively selected by a control circuit 6 at an RTN side and C16k, and through the AD converter 32 and the thinning filter 33, a ring trip processing is executed by a low pass filter 36b and a comparator 36c.
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